Make [] acceptable both for classes without constructors and
classes with a constructor that takes no arguments.

Closes GH-6336.

Closes GH-6335

These set the PGSQL_DML_EXEC flag by default.

This is an error that slipped in via 8d37c37bcdbf6fa99cd275413342457eeb2c664e.
pg_unescape_bytea() did not accept null in PHP 7.4, and it is not
meaningful for it to accept null now -- it will always fail, and now
with a misleading OOM message.

Closes GH-6294.

This makes it line up with pg_fetch_all_columns(), as well as
similar functions in other exts, such as mysqli_fetch_all().

The same error condition is a ValueError in mysqli, be consistent.

Additionally, do not display the argument name for these errors.
As the signatures are overloaded, the argument name may not match
the meaning at all.

The implementation did not check for PQunescapeBytea failure
correctly, because it checked for a null pointer after estrndup,
which certainly cannot happen. Inspection of the PGunescapeBytea
implementation has shown that this function can only fail on OOM,
so let's check for that explicitly and remove false as a possible
return type.

While we're here, avoid an unnecessary copy of the result.

These have been documentation-deprecated for a very long time,
make it official.

Closes GH-6149